Study of Broensted and Lewis Acid Sites in Phosphates, Silicates and Silica Gels with Molecular Sieve Properties

Kustov, L. М.; Zubkov, S. A.; Kazansky, V.B.; Bondar, L. A.

doi:10.1016/s0167-2991(08)61582-7

Cited by 15 publications

(4 citation statements)

References 4 publications

Supporting

Mentioning

Contrasting

Order By: Relevance

“…All bands below 3640 cm -1 are related to the stretching mode of bridged OH groups Si(OH)Al. The occurrence of HF and LF species has been already observed in other zeolitic systems, such as faujasite, SAPO-5, and SAPO-37, and assigned to Brønsted OH groups located in large cavities like the supercage (HF species) and in small cavities like sodalitic cages and hexagonal prisms of the FAU structure (LF species).…”

Section: Resultsmentioning

confidence: 76%

“…The weak peak at 3675 cm -1 is related to terminal OH species (such as P−OH and/or Al−OH groups), which are present in the sample in very small amounts, in contrast to what observed in other SAPO systems, e.g. SAPO-5 . The presence of such species is neglected in the following.…”

Section: Resultsmentioning

confidence: 94%

“…more acidic than the corresponding AlPO 4 systems, but usually less than zeolites . Sites like P−OH, Al−OH, and Si−OH groups show limited acidity. Substantial acidity is related to Si−O−Al bridges (coming from the substitution of silicon for phosphorous in the aluminophosphate lattice), which give rise, when protons neutralize the framework negative charges, to Brønsted sites structurally similar to those in zeolites, indicated hereafter as Si(OH)Al.…”

Section: Introductionmentioning

confidence: 99%

See 2 more Smart Citations

Spectroscopic Characterization of Hydroxyl Groups in SAPO-40. 1. Study of the Template-Free Samples and Their Interaction with Ammonia

et al. 1996

View full text Add to dashboard Cite

FTIR, MAS 1H-NMR, and molecular graphics data are reported concerning the hydroxyl species in a series of SAPO-40 samples with variable Si contents, as well as FTIR data concerning the interaction of ammonia with the different acid sites. Up to seven types of Si(OH)Al Brønsted sites are present, mainly differing by the O−H stretching frequency. Three high-frequency bands (3637−3624 cm-1) correspond to hydroxyls located in the 12-member channels and two low-frequency bands (3559 and 3528 cm-1) to OH species in eight-member rings and side pockets of the AFR structure. Two bands at exceptionally low frequency (3485 and 3445 cm-1 ) are due to OH species interacting with silica islands. All low-frequency bands behave with temperature as H-bonded species. All types of hydroxyls form ammonium ions, the thermal decomposition of which shows some difference in acidity among the OH species. IR evidence indicates that NH4 + species interact strongly with the basic oxygen atoms of the lattice. No Lewis sites were evidenced by ammonia adsorption.

show abstract

Section: Resultsmentioning

confidence: 76%

Section: Resultsmentioning

confidence: 94%

Section: Introductionmentioning

confidence: 99%

See 1 more Smart Citation

Spectroscopic Characterization of Hydroxyl Groups in SAPO-40. 1. Study of the Template-Free Samples and Their Interaction with Ammonia

et al. 1996

View full text Add to dashboard Cite

show abstract

“…Obviously, the stronger the O … H interaction in this complex, the larger the red shift of the C–H stretching vibration, and vice versa. The corresponding shifts in the C–D region are approximately equal to the value of the C–H shift divided by √2 [ 42 ]. For sample D the spectrum was also taken after heating in СО at 85 °С for 10 min.…”

Section: Methodsmentioning

confidence: 99%

A Study of Ziegler–Natta Propylene Polymerization Catalysts by Spectroscopic Methods

et al. 2017

View full text Add to dashboard Cite

Ziegler–Natta polymerization catalysts were characterized by a complex of surface- and bulk-sensitive methods (DRIFTS, XPS, ESR, and XAS = XANES + EXAFS). A diffuse-reflectance Fourier-transform IR spectroscopy (DRIFTS) study showed the presence of strong Lewis acid sites in different concentrations and absence of strong basic sites in the polymerization catalysts. X-ray photoelectron spectroscopy (XPS), electron-spin resonance (ESR), and (X-ray absorption near-edge structure (XANES) analysis revealed the presence of Ti4+, Ti3+, Ti2+, and Ti1+ species in the surface layers and in the bulk of catalysts. The samples under study differ drastically in terms of the number of ESR-visible paramagnetic sites. The EXAFS study shows the presence of a Cl atom as a nearest neighbor of the absorbing Ti atom.

show abstract

ChemInform Abstract: Generation of Acidity (Amount and Strength) in Silicoaluminophosphates (SAPO Zeolites). Examples of SAPO‐5, ‐11, ‐34 and ‐37

Barthomeuf

1995

ChemInform

View full text Add to dashboard Cite

show abstract

Study of Broensted and Lewis Acid Sites in Phosphates, Silicates and Silica Gels with Molecular Sieve Properties

Cited by 15 publications

References 4 publications

Spectroscopic Characterization of Hydroxyl Groups in SAPO-40. 1. Study of the Template-Free Samples and Their Interaction with Ammonia

Spectroscopic Characterization of Hydroxyl Groups in SAPO-40. 1. Study of the Template-Free Samples and Their Interaction with Ammonia

A Study of Ziegler–Natta Propylene Polymerization Catalysts by Spectroscopic Methods

ChemInform Abstract: Generation of Acidity (Amount and Strength) in Silicoaluminophosphates (SAPO Zeolites). Examples of SAPO‐5, ‐11, ‐34 and ‐37

Contact Info

Product

Resources

About